Process for impregnating fibrous sheets



PROCESS FOR IMPREGNATING FIBROUS SHEETS Filed July 13, 1962 NEEDLEPUNCHED NON-WOVEN WEB 0F SHRIIIIIABLE FIBERS IIIPIIEGNATING WITH AQUEOUSDISPERSION 0F POLYMER IIIPREGNATED WEB COAGULATING INPREGIIATED WEB WITHCOAGULATED IMPREGIIAIIT HEATIIIB SIIRUNIIEN IMPREGNATED WEB INVENTORSEMERSON B. FITZGERALD FRANCIS E. JENKINS BY 5 m 8 GM ATTORNEY UnitedStates Patent OfiFice Patented Jan. 11, 1966 3,228,786 PRUCES FORIMPREGNATING FIBRGUS SHEETS Emerson l3. FitzGerald and Francis E.Jenkins, Wilmington, Del., assignors to E. I. du Pont de Nemours andCompany, Wilmington, Del., a corporation of Delaware Filed July 13, W62,Ser. No. 209,791 4 Claims. (Cl. 117-62) This invention relates to amethod of impregnating shrinkable fibrous webs.

It has been proposed to make shoe upper material by preparing anon-woven web of heat shrinkable fibers, such as, 'e.g., polyethyleneterephthalate fibers, needle looming the web, shrinking the needled web,impregnating the nonwoven needled and shrunken web, finally applying amicroporous surface coating.

One of the problems encountered during the lasting operation whenforming shoes from material prepared as described above, is thedevelopment of roughness in those areas which requires some stretchingover the last such as in the toe and quarter areas of the shoe. Thisroughening has been associated with the pattern that results from theneedling of the non-woven web prior to impregnation.

It is an object of this invention to provide a process of preparing shoeupper material which involves impregnating and coating a non-woven webhaving a pattern on its surface prior to impregnating and coating whichis obscured by the impregnant and surface coating, and is not visuallyapparent when the impregnated and coated web is stretched as in the caseof toe and quarter lasting during shoe making.

The objective of this invention is accomplished by impregnating a heatshrinkable non-woven web capable of shrinking 2080% of its planar areaand having a pattern on its surface with an aqueous dispersion of apolymeric material, coagulating the dispersion in situ, heat shrinkingthe impregnated web 2070% of its planar area before the impregnant hasbeen allowed to dry and drying the impregnant. The more specific objectsof this invention are accomplished by surface coating the impregnatedweb referred to above wherein the pattern on the surface of. thenon-woven web is not discernible when the coated fabric is stretched asin shoe lasting.

The drawing illustrates a flow sheet of the process.

The degree of roughening or absence of roughening encountered in the toeand quarter area of the shoes made with an impregnated and coated shrunknon-woven web, having a pattern on its surface prior to impregnating andcoating, is dependent upon the amount of impregnant introduced into theWeb prior to the shrinking of the web. The amount of impregnant alsoaffects the degree of shrinking as does the temperature and method ofheat shrinking. As the amount of the non-volatile components of theimpregnant introduced into the web increases the amount of heatshrinking of the non-woven web decreases. The amount of non-volatileimpregnant introduced into the web is controlled primarily by theconcentration of the solids (non-volatile components) in the dispersion.The maximum amount of area shrinkage of a web capable of 90% areashrinkage is reduced to about 60% area shrinkage when it is saturatedwith an aqueous dispersion having a concentration of non-volatilecomponents of about 30%. Non-woven webs impregnated with dispersionshaving lower solids concentrations will permit greater amount of areashrinkage with the same heat shrinkable webs.

The amount of impregnant which is introduced into the web is determinedto a large extent by the end use of the product. For shoe uppers, thepreferred amount of dry impregnant, based on the weight of the fibers,is about 100 to 400% and the particularly preferred range is about 200to 300%, same weight basis. If the amount of dry impregnant in the webis less than about based on the weight of the fibers, roughening isencountered when the impregnated and coated web is subjected to about35% stretching in the direction of width and/or length. The upper limitof the amount of dry impregnant is controlled by the concentration ofthe non-volatile components in the impregnating compositions.Concentrations greater than that required to introduce about 400% dryimpregnant, based on the weight of the fibers, do not result in uniformimpregnation.

Impregnating the heat shrinkable non-woven webs with an aqueousdispersion prior to heat shrinking has other advantages besides reducingthe roughening encountered when the impregnated and coated sheets arestretched as encountered in shoe lasting operations. Impregnation ismore uniform and faster with the aqueous dispersions prior to heatshrinking due to the rapid wicking of the less dense web. It is alsopossible to achieve a higher ratio of impregnant to fiber byimpregnating prior to shrinking due to the more open structure of theweb.

The use of an aqueous dispersion as the impregnant has still furtheradvantages over solutions of polymer in organic solvents in that it ispossible to use much higher solids concentration of aqueous dispersionsat lower viscosity to achieve thorough and uniform impregnation of theweb; no solvent recovery or toxicity problems are en countered with theaqueous dispersions; water does not destroy the shrinkability of theshrinkable fibers as do most organic liquids; and it is much easier toimpregnate fragile non-woven webs with low viscosity dispersions thanwith high viscosity solutions of the same polymer.

The aqueous dispersion impregnants can be coagulated within the web by avariety of techniques including freeze coagulating, immersing the web inan aqueous solution of an electrolyte, heating the impregnated web, andin the case of non-coalescible dispersions allowing the impregnatingcomposition to dry at room temperature.

In making moisture permeable shoe upper material by impregnating a heatshrinkable non-woven web with an aqueous dispersion, the freezecoagulation is particularly preferred in that the coagulum is depositeduniformly throughout the web in a highly porous form thus aiding thepermeability of the final product. There is also very little, if any,migration of the impregnant, during the freeze coagulation, drying, andheat shrinking of the nonwoven web.

The aqueous dispersions which have been found to be particularly usefulin practicing this invention are the aqueous dispersions of rubberylow-modulus elastomers, such as neoprene (polychloroprene), butylrubber, Hycar (copolymer of butadiene and acrylonitrile), Buna S(copolymer of butadiene and styrene), natural rubber, aqueousdispersions of thermoplastic polymers and copolymers, such as, e.g.,Geon 351 (plasticized polyvinyl chloride), oil modified alkyd resin,acrylic resins and methacrylic resins, as well as various mixtures ofthe aforementioned dispersions.

The particularly preferred heat shrinkable fiber for forming thenon-woven web is composed of polyethylene terephthalate. Other usefulheat shrinkable fibers include those composed of cellulose acetate,nylon, 40/60 copolymer of acrylonitrile and vinyl chloride,polyethylene, polypropylene, polystyrene and polytetrafluoroethylene.Blends of the foregoing heat shrinkable fibers are also useful forforming the non-woven web. It is also possible to blend heat shrinkablefibers with nonshrinkable fibers in which the shrinkable fibersrepresent at least 50% of the fibers in the non-woven web. EX- amples ofnon-shrinkable fibers are any of the foregoing shrinkable fibers whichhave been shrunk prior to forming the non-woven web, as well as naturalfibers, including cotton, jute, flax, wool, etc.

Example I A fluffy, loosely bound, non-woven web weighing 14.9 ouncesper square yard and composed of polyethylene terephthalate fibers of1.25 denier, formed on a card and crosslapper, was passed through aneedle loom six times. The density of the needle punches was about 1536per square inch. The needle punched web weighed 11.9 ounces per squareyard and possessed a very pronounced needle pattern having aherringbone-like appearance.

The needled web was immersed in an aqueous latex of neoprene containing30% non-volatile ingredients, including polychloroprene, antioxidants,curing agents, accelerators, etc., as described in Example 1 of FrenchPatent 1,289,754. The web was saturated and uniformly impregnatedthroughout with the aqueous latex. The impregnated web was removed fromthe impregnating bath and the excess latex was allowed to drain from theweb. Before the impregnant was allowed to dry, the impregnated Web wasexposed to a temperature of 40 F. until the impregnant was frozen andcoagulated throughout the web. After the impregnant was freezecoagulated and thawed, the excess water was allowed to drain therefrom.Before the impregnant was allowed to dry completely, the impregnated Webwas immersed in a water bath heated to 65 C. for about 5 minutes duringwhich time it was shrunk 63% of its planar area. The shrunkenimpregnated web was thoroughly washed with water to remove any watersoluble ingredients deposited in the web from the latex, such asdispersants. The washed web was dried in an oven for 1 hour at 100 C.and then heated for 30 minutes at 140 C. to cure the neopreneimpregnant. The dry impregnant was deposited throughout the web in aporous condition with both micro and macro pores being present.

The dry impregnated web was buffed on each side to remove the skinsurface of the impregnant. The web at this stage, about 150 mils thick,was skived into three layers, each about 50 mils thick.

A control sample was made in the same manner and with the sameingredients as described above except the impregnating step was carriedout after the web shrinking step and the temperature of the water duringthe shrinking step was 63 C. instead of 65 C. in order to obtain acomparable amount of shrinkage. The amount of planar shrinkage of theunimpregnated web for the control sample was 50%.

The product produced in accordance with Example I and the control forExample I had the following physical properties:

Example I Control for Example I Density, g./cc 0. 764 0. 43 Thicknemils"- 50 50 Permeability Value 6, 900 8, 700 Elongation at Break:

Machine Direction, percent 240 150 Cross Machine Direction, percent- 230140 Strength at Break:

Machine Direction, p.s.i 1, 600 1, 000 Cross Machine Direction, p.s.i950 1, 100 Initial Modulus:

Machine Direction, p.s.i 2, 800 1, 900 Cross Machine Direction, p.s.i 1,700 1, 900 Tonguer'lear (Pounds per Inch T ckness) Machine Direction 12898 Cross Machine Direction 180 105 The permeability values were carriedout by filling a three inch diameter crystallizing dish with 12 meshcalcium chloride, covering the dish with membrane of the substance to betested and placing the covered dish in an atmosphere of high humidity(23 C. and 90% relative humidity). The assemblage is weighed atintervals and the equilibrium rate of sorption is recorded as grams ofwater per 100 sq. meters of surface per hour which is the leatherpermeability value. This is a modification of a test developed by theBureau of Standards, Kanagy & Vickers, J. Res. Nat. Bureau of Standards,44, 347-62, 1950 (April).

The impregnated product as described above, before and after the skin onthe surface is removed, as well as after skiving, is an article ofcommerce and has a variety of uses such as gaskets, diaphragms, bearingseals, paulins, etc. The buffed and skived product is particularlyuseful as a substrate for surface coatings in the making of shoe uppermaterials as described more fully hereinafter.

The 50 mil thick impregnated substrate produced in accordance withExample I and the 50 mil thick control materials were each coated on oneside with a surface coating composition described below. Sufiicientcomposition was applied to deposit a dry surface film about 10 milsthick. The surface coating composition consisted of about 10.5% of apolyurethane elastomer, 5.7 parts of polyvinyl chloride and 83.8 partsof N,N-dimethyl formamide (referred to hereinafter as dimethylformamide). The coating composition was prepared by mixing 52.5 parts ofa 20% solution of the polyurethane elastomer dissolved in dimethylformamide with 47.5 parts of a 12% solution of polyvinyl chloridedissolved in dimethyl formamide. Suffiicent non-solvent for thepolymers, such as an /20 mixture of dimethyl formamide and water, wasadded to the mixture of solution to form an incipient gel.

The 20% solution of polyurethane elastomer was prepared by first mixing3343 parts of polytetramethylene ether glycol of about 1000 molecularweight with 291 parts of tolylene-2,4-diisocyanate and heating themixture for 3 hours at C. Then 2485 parts of the resulting lhydroxylterminated dimer were mixed with 570 parts of methylene-bis-(4-phenylisocyanate). This mixture was heated for one hour at 80 C., yielding aprepolymer with isocyanate groups. The prepolymer was dissolved in10,000 parts of dimethyl formamide and the resulting solution was addedslowly toa solution consisting of 50 parts of a polymer chain extenderdissolved in 1710 parts of dimethyl formamide. The chain extenderconsisted of N-methyl-bis-amino propyla-mine and hydrazine hydrate in amolar ratio of 40:60. The re sulting reaction mixture was stirred at 40C. for 30 minutes to form a polyurethane solution having a viscosity ofabout 115 poises and a polymer content of about 20%.

Immediately after the surface coating composition was applied to thesubstrate and before any appreciable amount of dimethyl formamide wasallowed to evaporate therefrom the coated substrate was immersed inwater at room temperature for 2 hours. During this water immersion step,the coating solution was coagulated and converted into a gelatinouspolymeric layer having a cellular structure of interconnectingmicropores and substantially all of the dimethyl formamide was extractedfrom the solution coating.

Next the coated fabric was subjected to steam for about 15 minutes thendried at C. in dry heat zone. When dry, the surface coating had a Whitemilky appearance and was highly permeable to water vapor.

The dry coated fabric was next immersed for 30 minutes in a boilingaqueous dye bath containing 5% of chromed monoazo black dye identifiedas C1-15711 (Colour Index number) in Colour Index, Second Edition, vol.3, 1957, American Association of Textile Chemists and Colorants.

The dyed coated fabric is next scoured for 15 minutes in a boilingaqueous scouring bath containing 0.3% of a non-ionic detergent based onthe weight of the water. The detergent was the condensation productobtained by reacting 20 moles of ethylenic oxide with one mol of a C-l8aliphatic monohydroxy alcohol.

The dried and scoured impregnated and coated fabric had a deep blackcolor. It Was highly permeable to moisture vapor, tough, abrasionresistant and eminently suited for use as mens and womens shoe uppers.

Both coated substrates, i.e., the Example I and its control, werefabricated into mens dress shoes by the usual shoe making techniqueswhich involved stretching the coated substrates over a last and holdingthe material in the stretched condition during the shoe makingoperation.

In the case of the control, the needle pattern in the non-woven webwhich had been obscured by the impregnating and surface coatingcompositions was caused to reappear in the surface coating uponstretching during lasting of the shoes and remained in the areas ofgreatest stretch, such as, the toe and quarter portions of the shoeafter the shoe was separated from the last and the stress removed.

In the case of the Example I material, the needle pattern in thenon-woven web was likewise obscured by the impregnant and surfacecoating. The pattern was not discernible in the surface coating duringor after the shoe lasting operations.

On an evenly graduated scale where zero represents complete absence ofneedle pattern in the surface coating when subjected to stress duringshoe making operation and 6 represents severe roughening, i.e.,appearance of needle pattern, the Example I impregnated and coatedsubstrate had a rating of 1 and the control for Example 1 had a ratingof 6.

Example 11 Example I was repeated except a fluffy, loosely boundnon-woven web weighing 13.3 ounces per square yard of polyethyleneterephthalate fibers of 1.25 denier, formed on a card and cross-lapper,was passed through a needle loom nine times. The density of the needlepunch was 2750 per square inch. The weight of the web after needlepunching was 10.3 ounces per square yard and possessed a very pronouncedneedle pattern having a herringbonelike appearance.

A further variation in the procedure of this Example II from thatdescribed in Example I was that the temperature of the hot water bathemployed for the shrinking of the impregnated web was 70 C. instead of65 C. The impregnated web of Example II shrunk 63% of its planar area ascompared to 53% for the impregnated web of Example I.

A control for Example II was prepared in the same manner and with thesame ingredients as employed for Example 11, the only difference beingthe shrinking step was carried out before the impregnating step.

The product produced in accordance with Example II and the control forExample II had the following physi- The impregnated webs of Example IIand the control for Example 11 were coated with the same composition andsame manner as described above for Example I and then formed into mensshoes by the usual lasting processes. The needle pattern which had beenobscured by the impregnating and surface coating composition in the 6case of the Example II material was hardly discernible in that area ofthe shoe upper which had been stretched during lasting, i.e., the toeand quarter areas and had a rating of 1 on the scale mentioned above,whereas the control material had a rating of 6.

Example III A non-woven web of polyethylene terephthalate fiberscomposed of 0.8 denier crimped staple was formed on a card andcross-lapper. The Web Weighed 9.0 ounces per square yard. It was passedthrough a needle loom to orient some of the fibers perpendicular to theplane of the web to give it reinforcement.

The Web was immersed in the following impregnating composition until itwas completely saturated:

Parts by weight Neoprene latex (Example IFrench Patent 1,289,754) 180.0Water 157.0

Calco A-2246 (33% aqueous dispersion of 2,2-

methylene bis (6 tertiary butyl paracresol) 5.4 Zinc oxide aqueoussolution) 9.0 Aquarex SMO (33% aqueous dispersion sodium salt ofsulfated methyl oleate) 8.1 Tepidone (50% aqueous solution sodiumdibutyl dithiocarbamate) 1.8 Thiocarbanalide (33% aqueous dispersion)2.7 Geon Latex 351 vinyl chloride polymer (57% aqueous dispersion) 10.0Water 13.4

The impregnated web was freeze-thaw coagulated in the same mannerdescribed above in Example I. Before the thawed impregnant was allowedto dry, the impregnated Web was immersed in water, heated to 70 C. andallowed to remain therein for 15 minutes after which it was removed anddried. The impregnated web shrunk of its original planar area during theexposure to the hot water. The impregnant was cured at 120 C. forminutes. The fiber to hinder ratio was to 274.

The cured impregnated web was sanded on both sides to remove the skin ofthe excess impregnant. The impregnated product was microporous, smoothand free of macro voids. The product was flexible and on 35% transverseand on 35% longitudinal stretching, no roughening was observed, i.e., ithad a roughening value of zero on the scale described above. Thestretched sample returned to its original dimension after the stress wasremoved.

The impregnated web was ideally suited as a substrate for surfacecoating in the manufacture of shoe upper material.

Good results as to non-roughening, i.e., absence of needle pattern onthe surface of the impregnated and coated non-woven Webs produced inaccordance with this invention when formed into shoes by the standardshoe making techniques are obtained when the aqueous dispersions containabout 20-60% solids. Dispersions containing 25-40% solids are preferredand best results are obtained with about 30% solids. If higherconcentrations are used, the area shrinkage of the impregnated webs isreduced and there is also a reduction in roughening of the coatingduring the lasting operation when the coated Web is formed into shoes,although other valuable properties are decreased, such as unsightlyappearance in the vamp area of the shoe when flexed, which is referredto as poor leather break.

At lower concentrations of the latex impregnant, there is lessimpregnant introduced into the web, and there is an increase in theshrinkage of the impregnated nonwoven web accompanied by an increase inroughening (i.e., appearance of needle pattern) during and after thelasting operation of shoe manufacture.

A coated Web having a roughening value greater than 2 is not consideredcommercially acceptable for high grade shoe uppers.

It Will be understood, however, that the products made in accordancewith this invention having a roughening value greater than 2 are usefulfor other end uses where the roughening on stretching is notdetrimental, such as e.g., gaskets, fuel pumps, upholstery, pocketbooks,mens and ladies jackets, paulins, etc.

We claim:

1. A process Which comprises:

(a) preparing a non-Woven web of fibers, said Web being capable ofshrinking 2080% of its planar area and having a needle pattern on itssurface,

(b) impregnating said Web 'with an aqueous dispersion of a polymericmaterial,

(c) coagulating said aqueous dispersion impregnant,

and

(d) subjecting said impregnated Web to an elevated temperature Whichcauses it to shrink 2070% of its planar area before the impregnantdries.

2. The method of claim 1 in which step (d) is carried out by immersingthe impregnated web in Water at a temperature of 63 C. to 90 C.

3. The method of claim 1 in which the coagulation step is carried out byfreezing the aqueous suspending medium for the dispersant.

4. The method of claim 1 which involves an additional step of applying asurface coating to the impregnated Web.

References Cited by the Examiner UNITED STATES PATENTS 2,444,124 6/1948Wedler 117-62 2,723,935 11/1955 Rodman 161- 166 2,910,763 11/1959Lauterbach 161189 X 2,930,106 3/1960 Wrotnowski et a1. 117-440 2,973,2842/1961 Semegen l17-l40 XR 3,067,482 12/ 1961 Hollowell 17763 XR3,100,721 8/1963 Holden 117135.5

FOREIGN PATENTS 931,374 7/1963 Great Britain.

WILLIAM D. MARTIN, Primary Examiner.

1. A PROCESS WHICH COMPRISES: (A) PREPARING A NON-WOVEN WEB OF FIBERSSAID WEB BEING CAPABLE OF SHRINKING 20-80% OF ITS PLANAR AREA AND HAVINGA NEEDLE PATTERN ON ITS SURFACE, (B) IMPREGNATING SAID WEB WITH ANAQUEOUS DISPERSION OF A POLYMERIC KMATERIAL, (C) COAGULATING SAIDAQUEOUS DISPERSION IMPREGRANT, AND (D) SUBJECTING SAID IMPREGNATED WEBTO AN ELEVATED TEMPERATURE WHICH CAUSES IT TO SHRINK 20-70% OF ITSPLANAR AREA BEFORE THE IMPREGNANT DRIES.